Driving system comprising a reluctance motor having both position and speed feedback

ABSTRACT

A reluctance motor has a stator with a plurality of stator pole bodies arranged circumferentially one after the other and supporting a body and a rotor with a plurality of rotor poles arranged circumferentially one after the other, so that a given turning movement of the rotor causes the permeance between a stator pole and a rotor pole to increase from a minimum value to a maximum value upon half the movement, and then to decrease progressively to the minimum value. The winding is connected to a current source, the voltage of which during motor operation is synchronized in such a way that the average value of the current flowing through the winding while the permeance is increasing is greater than while it is decreasing. The current source is a controlled semiconductor converter connected between a network and a winding and which forms a part of a controlled circuit and delivers a direct current. A current comparison device which controls the converter compares the difference between the current flow through the converter and a varying reference value. This varying reference value is furnished by the combination of a constant reference value and a second reference value, the supply of which is controlled by a switching device operating synchronously with the rotation of the motor. The reference value supplied to the switching device is a combination of a predetermined reference value and a value dependent on the speed of rotation. A phase-advancing circuit is provided to advance the operation of the switch means proportionately to the speed of rotation.

United States atent 1 [111 Means Torok [451 July 3, 1973 DRIVING SYSTEMCOMPRISING A [57] ABSTRACT RELUCTANCE MOTOR HAVING BOTH POSITION ANDSPEED FEEDBACK [75] Inventor: Vilmos Torok, Vasteras, Sweden [73]Assignee: Allmanna Svenska Elektriska Aktiebolaget, Vasteras, Sweden[22] Filed: Nov. 25, 1970 [21] Appl. No.2 92,729

[30] Foreign Application Priority Data Nov. 26, 1969 Sweden 16232/69[52] US. Cl 318/254, 318/327, 318/231 [51] Int. Cl. H021: 29/00 [58]Field of Search 318/138, 254, 327,

[56] References Cited UNITED STATES PATENTS 3,127,548 3/1964 Van Emden318/696 3,271,649 9/1966 Juergensen 318/138 X 3,612,973 10/1971Kuniyoshi 318/254 3,512,067 5/1970 Landau 318/231 X 3,418,550 12/1968Kolatorowicz et a1 318/254 X 3,440,506 4/1969 Krestel et a1 318/254 X3,529,220 9/1970 Kobayahi et a1 318/254 X 3,577,049 5/1971 Madurski318/254 3,593,083 7/1971 Blaschke 318/231 3,500,158 3/1970 Landau et a1318/227 Primary Examiner-G. R. Simmons Attorney-Jennings Bailey, Jr.

A reluctance motor has a stator with a plurality of stator pole bodiesarranged circumferentially one after the other and supporting a body anda rotor with a plurality of rotor poles arranged circumferentially oneafter the other, so that a given turning movement of the rotor causesthe permeance between a stator pole and a rotor pole to increase from aminimum value to a maximum value upon half the movement, and then todecrease progressively to the minimum value. The winding is connected toa current source, the voltage of which during motor operation issynchronized in such a way that the average value of the current flowingthrough the winding while the permeance is increasing is greater thanwhile it is decreasing.

The current source is a controlled semiconductor converter connectedbetween a network and a winding and which forms a part of a controlledcircuit and delivers a direct current. A current comparison device whichcontrols the converter compares the difference between the current flowthrough the converter and a varying reference value. This varyingreference value is furnished by the combination of a constant referencevalue and a second reference value, the supply of which is controlled bya switching device operating synchronously with the rotation of themotor. The reference value supplied to the switching device is acombination of a predetermined reference value and a value dependent onthe speed of rotation. A phase-advancing circuit is provided to advancethe operation of the switch means proportionately to the speed ofrotation.

2 Claims, 18 Drawing Figures PHASE "SH/F TING l DEV/CE Z POS/T/ONRESPONS/VE DE VICE 7r TACHOME TE R Patefited july 3, 1973 5 Sheets-Sheet1 Fig. 2

INVENTOR. BY VII-M 0s fixb K Patented July 3,1973 3,743,906

5 Sheets-Shoot 2 Fig 60 JNVENTOR.

V! LMOS 'T'ORQ Patented July 3, 1973 5 Sheets-Shoat 4- I W o I m R M I III-Iillllll;

Patented July 3, 1973 5 Sheets-Shoot 5 INVENTOR.

V l (PM 05 TE) Q 6 K QQAWMLW DRIVING SYSTEM COMPRISING A RELUCTANCEMOTOR HAVING BOTH POSITION AND SPEED FEEDBACK BACKGROUND OF THEINVENTION 1. Field of the Invention The present invention relates to adriving system comprising a reluctance motor, the stator of which has anumber of stator pole bodies arranged tangentially one after the otherand supporting a winding, and the rotor of which has a plurality ofrotor poles arranged tangentially one after the other, wherein a certainturning movement of the rotor causes the permeance between a stator poleand a rotor pole to increase from a minimum value to a maximum valueupon half the movement, and then to decrease progressively to saidminimum value, said winding being connected to a current source, thevoltage of which during motor operation is synchronized with the rotormovement in such a way that the average value of the current flowingthrough the winding while the permeance is increasing is greater thanwhile it is decreasing.

2. The Prior Art Such driving systems are known (for example throughGerman published specification No. 1,102,262) in embodiments intendedfor purposes requiring little power. The synchronized current sourcethen consists of a direct current source in series with a circuitbreaker driven by the rotor movement. The contacts of the circuitbreaker are separated during intervals when said permeance is decreasingso that the current through the winding is broken, or at least reduced.A necessary condition for motor operation to be obtained in a reluctancemotor is that the magnetic flux through the poles during said intervalsof decreasing permeance is reduced. In the devices described above thisis done by consuming a considerable part of the magnetic energy storedin the pole system at maximum flux in the form of arc effect in thecircuit breaker. This means that the driving system is very inefficientand its usefulness is therefore very limited. Furthermore, a reliablebreaker operating in the manner described above can hardly bemanufactured at reasonable cost if the motor power is more than 0.5 kW.

Attempts have also been made to develop a reluctance machine forrelatively high power. Such a ma- I chine is described in the BritishPat. No. 1,099,010,

that is, a reluctance machine intended to be driven as a synchronousmachine. The machine requires no switching means. It is provided with anoperating winding, intended to be connected directly to an alternatingcurrent network, and also with a direct current winding. The necessarydifference between the magnetic attraction at increasing and decreasingpermeance is obtained by adding the AC flux and the DC flux in the airgap. The flux paths must therefore be arranged in such a way that the ACflux is not surrounded by the DC winding, thus making the design of themachine complicated and expensive. However, the poles have thealternating flux and the flux generated by the DC winding flowingthrough them, which means that the amount of material used per powerunit is greater than with conventional machines.

The machine is provided with a special magnetic layer on the rotor orstator pole faces, and this magnetic layer has a saturation flux densitywhich is substantially lower than that of other parts of the magneticflux circuit. In this way the pole flux is made dependent on theoverlapping between stator and rotor pole faces, and strongly responsiveto a changed degree of overlapping even when the overlapping is rathergreat, for example more than half its maximum value.

With relatively large machines made with a high degree of utilization asregards magnetic material, the value of the pole flux increase whichoccurs upon a certain increase of the degree of pole overlapping can bepractically constant in a range of overlapping corresponding to adominating part of the tangential extension of a pole, provided thepole, in accordance with conventional reluctance motor designprinciples, is constructed without any increase of the pole section nearthe pole face.

SUMMARY OF THE INVENTION A driving system according to the invention isintended to include a reluctance motor which, even when dimensioned forhigh power, can be made with substantially the same simple design asmost of the conventional reluctance motors, the expensive andcomplicated structure of the machine described above being avoided.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings:

FIG. 1 shows the demand for regulating current and voltage in a DCmotor;

FIG. 2 shows the demand for regulating a synchronous and an asynchronousmotor;

FIG. 3 shows the demand for regulating a DC reluctance motor;

FIG. 4 shows the working range for a controlled current rectifier incollaboration with an alternating current source;

FIG. 5 is a sectional view through a reluctance motor perpendicularly tothe shaft;

FIG. 6 is a sectional view along the line AA in FIG. 5;-

FIG. 6a shows a view of a reluctance motor comprising three motor unitsaccording to FIGS. 5 and 6;

FIG. 5a shows the orientation of the rotor in the phase Y motor unit;

FIG. 5b shows the same for phase Z;

FIG. 7 shows an embodiment of a driving system according to theinvention;

FIG. 7A shows the output signal of the switching device in pull-inposition and in dependence on the output signal of the speed regulatorunit 15;

FIG. 7B shows the same in draw-out position;

FIG. 7C shows current and voltage progress for a motor unit duringdriving;

FIG. 7D shows the same during braking;

FIG. 8 is a detailed diagram of the connections with reference to FIG. 7and it shows the internal connection of the devices which in FIG. 7 isindicated as blocks or circles;

FIG. 9 shows a detailed diagram of the semiconductor 10 of FIG. 7 whenthe reluctance motor'is driven from a one-phase AC network;

FIG. 9A shows the same when the feeding network is a three-phase one;

FIG. 10 shows the same applied to a DC network.

Hitherto no driving system has been developed which in any way altersthe conception expressed in known textbooks and manuals, namely that inview of its low efficiency and utilization of material the reluctancemotor is not suitable for driving systems having relatively high power.

Since the arrival of semiconductor rectifiers for strong current on themarket, a considerable number of advanced driving systems have beendeveloped, for example systems with continuous speed control andregenerative brakin'g, which are. based on the combination of controlledsemiconductor rectifiers and rotating electric machines. Since therectifier equipment in such systems is a considerable portion of thecosts, it is naturally desirable to utilize it to the fullest extent andthe rotating machine cooperating with the rectifiers must therefore beone of high efficiency. It is then easy to understand that thereluctance motor has therefore hardly seemed to the experts to be anattractive alternative in the choice of the type of machine for arectifiercontrolled driving system when this is to be dimensioned forrelatively high power, for example a power greater than 0.5 kW.

The knowledge upon which the present application for patent is based hasbeen acquired by the inventor through a systematic analysis carried outin order to obtain a diagrammatic survey concerning the variety ofcurrent and/or voltage directions needed for different modes ofoperation for different types of motors. FIGS. 1, 2 and 3 of theaccompanying drawings give graphic illustrations for DC, synchronous orasynchronous motors, and for a reluctance motor, respectively, Udesignating voltage and 1 current. It is seen that a synchronous orasynchronous motor requires both current and voltage suppliable in twodifferent directions and that the current in a DC motor must bereversible if regenerative braking is to be possible. As indicated bydotted lines in FIG. 1, in the latter cases even the supplied voltagemust be reversible if the motor is to be able to reverse. A reluctancemotor operates as a'motor during the above-mentioned permeance increaseand can operate as generator in the interval when permeance decrease istaking place. The current direction in the winding is then unchangedupon a transfer from permeance increase to permeance decrease sinceduring permeance decrease a voltage is induced in the winding whichtends to maintain the flux. If, during permeance decrease, the currentsource connected to the winding is operating with reversed voltagedirection, this will mean that the reluctance motor returns power to thecurrent source during the permeance decreasing interval. Regenerativebraking can be achieved by varying the absolute value of the imposedvoltage in such a way that the power fed back is greater than thatsupplied to the motor in a subsequent interval. The direction ofrotation of the motor is independent of the direction of the current andvoltage delivered by the current source.

Thus, with a reluctance machine, all types of operation can be obtainedwith the same current direction in the winding, as indicated in FIG. 3.

If a controlled current rectifier is connected to a current source whichdelivers current through the current converter to a load, the current inthe load circuit can only have one direction and it can continue to floweven when the voltage of the current source alters direction, assumingthat a sufficiently high voltage counteracting the voltage of thecurrent source arises simultaneously in the circuit, for example due toinduction.

A controlled current rectifier in cooperation with a current sourcehaving alternating voltage thus has a working range which can beillustrated graphicly as shown in FIG. 4, where U designates voltage andI current 0n comparing FIG. 4 with FIGS. 1, 2 and 3, it is seen thatFIG. 3 conforms with FIG. 4, which means that the reluctance motor, andonly this type of motor, has those properties required in order toattain almost unlimited flexibility in operation with the simpleconverter equipment described above.

A driving system according to the invention is characterized in that thedriving means is intended for a power of at least 0.5 kW and comprises acontrolled semiconductor converter connected between a network and themotor winding, and being part of a closed control circuit, saidsemiconductor converter delivering a pulsing direct current, acurrent-comparison device being included in said control circuit and awinding current transducer connected to the comparison device, and aswitching device controlled by pulses and arranged as reference valueemitter, to change from a first to a second and higher current referencevalue, and vice versa, and a position-responsive device arranged to giveswitching signals to said switching device with a time intervalcorresponding to half of said rotor turning movement, wherein saidsemiconductor converter, in a manner known per se, is arranged tooperate with constant current direction and alternating power directionin the winding, power being returned to the network in the time intervalwhen the magnetic flux linked with the winding is reduced by reductionof said permeance.

A driving system according to the invention has, in

comparison with similar allround driving systems having semiconductorr'ectifiers in combination with one or more rotating machines, theadvantage that therequired power can be supplied to the motor by a muchsimpler and cheaper rectifier equipment. It might be feared that thetendency towards price reduction, which is obtained since the number ofsemiconductor components is unusually low, would to a great extent beoffset by the relatively high brutto power needed by the reluctancemotor because of its well-know low efficiency. However, experiments haveshown that not only is it possible with a driving system according tothe invention to fulfil all reasonable control requirements with anunusually low number of semiconductor rectifiers, but also that themethod of operation used gives the reluctance motor an efficiency atleast as great as that of a corresponding asynchronous machine. The highefficiency may to a great extent be putdown to the fact that powergenerated in the motor during intervals of generator effect (normally inintervals with decreasing permeance between rotor and stator) is fedback to the current source with the help of the semiconductor devicewhich is part of the driving system.

it has been found that the degree of utilization of the motor accordingto the invention is at least as high as an asynchronous motor ofconventional design, and since the constructional design is hardlycomplicated it is possible even for very high motor power, for example1000 kW, to manufacture the motor at a price which is below that ofconventional machines.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the following the inventionwill be described with reference to FIGS. 5 of the drawings.

In FIGS. 5 and 6, 1 designates the rotor shaft, 2 a pole-holder attachedon the rotor shaft, which holder may be of steel or non-magneticmaterial, and which has a plurality of rotor poles 3 uniformlydistributed in tangential direction, the pole gaps between having anaverage width of about 40 percent of the average pole distribution. Onlytwo poles are shown in the drawing. A rigid stator casing 4 supports aplurality of yokeshaped stator poles 5 which are arranged with the samedistribution as the rotor poles. When a stator pole 5 and a rotor pole 3are opposite each other, as in the drawing, they form together acomplete magnetic circuit. The circuit then has its maximum value andthis decreases as the rotor turns to a minimum value which is obtainedwhen a rotor pole is between two stator poles. Contrary to what is usualin, for example, DC machines and synchronous machines, the pole width isnot greater at the airgap than at other pole parts. When a stator poleand a rotor pole start to overlap local saturation tends always to occurnear the overlapping poles surfaces even at a relatively low rate ofampere turns. With the above design of the poles, shown in the drawing,it is ensured that, even when there is considerable overlapping,saturation occurring in the overlapping zone can always occur at astator ampere turn which is less than that required for saturation ofthe majority of the pole. The advantage is thus gained that an extremelyuniform increase in permeance is obtained while the rotor is turningfrom zero to 100 percent overlap. The motor is provided with only onewinding, the stator winding 6, which is annular with tangential turnsand is arranged to partly be surrounded by each stator pole.

With the object of achieving uniform and smooth running and ensuringstarting at all angles, a motor may preferably be used which is composedof a plurality of units of the same construction as that shown in FIGS.5 and 6. A machine constructed from the unit motors X, Y, Z is shown inFIG. 6a. The stators of the three identical motor units have exactly thesame angle in relation to the common shaft lxyz. An axial plane A-Athrough the center of the shaft and the middle of the pole of the statorpole 5 also runs centrally through the stator poles 5a and 5b. The threerotors are attached on the shaft 1 at different angles as shown in FIGS.5, 5a and 5b. When the rotor shown in FIG. 5 has one rotor pole exactlybelow the stator pole 5, the motor Y has one rotor pole in such aposition that its central plane is displaced 10 in relation to the axialplane AA and the motor Z has a corresponding displacement of All therotors have a pole pitch of The stator of a motor unit does notnecessarily have to be shaped as shown in FIGS. 5 and 6. In principle, astator may even be used having north and south poles arrangedalternatively in tangential direction and each provided with a fieldwinding, the stator winding then consisting of a plurality of coilsconnected together. Instead of several stator bodies, a single statorring may be used having a plurality of phase windings, the number ofthese being equal tothe number of stator bodies in the firstalternative. For example a motor according to FIG. 3 in US. Pat. No.3,062,979 may be used if opposite coils are connected to constitutephase windings. In this case there would be two phase windings.

The embodiment of the invention shown in FIG. 8 concerns a systemcomprising a motor of a similar type to that shown in FIG. 6a, Le, amotor which is composed of three motor units. All the motor windings areshown and the symbolically indicated rotor should be considered ascomprising three rotor units attached on the same shaft. For the sake ofsimplicity only the poles of one of the rotor units are shown in therotor symbol. Magnitudes and components corresponding to the variousmotor units are designated with X, Y and Z, respectively. Thus a closedcontrol circuit particularly belonging to the motor unit y is surroundedby a dotted frame and designated Y. Corresponding and exactly similarcontrol circuits are arranged for the motor units X and Z as well, butthese are not shown in the figure. The designations used are as follows:

Iy current through winding Y I, current reference for winding Y Idesired current value for a half period with decreasing permeance I 1desired current value for a half period with increasing permeance nspeed of motor m; desired value for speed In FIG. 7 the reluctance motoris designated 7, its rotor 7r and the stator winding 8. The stator isnot otherwise shown. The winding 8 of each motor unit is connected to anAC network 9 via a controlled semiconductor converter 10 which convertsthe alternating current to DC pulses of constant length. A magnitudeproportional to the winding current is taken out from the currenttransducer 19 and compared in the comparison device 12 with a currentreference value, thedifference being supplied to the input side of theregulator 11 connected to the control circuit of the converter 10. The

regulator 11 consists essentially of an amplifier 11a with feedbackthrough a capacitor 11b and a resistor 11c and a'series resistor 11d.

The motor 7 consisting of three motor units is provided with a positionresponsive means 20 in the form of a device giving signal pulses,through a phase advancing determinator 23 which may be omitted in somecases, to the switching device 13 when the stator and rotor poles aresubstantially opposite each other and in positions when the rotor polesare substantially between two stator poles. Any convenient positionresponsive means can be used, for example a rotor driven timer which hasa magnetic circuit, the permeance having a value dependent on the rotorposition, or a photoelectric device. The switching device 13 has twoinput circuits for current references, one circuit being connected to amanually adjustable reference value emitter l4 and the other to theoutput side of a regulator unit 15 similar in construction to the unit11, its input side being supplied from a comparison device 16 with thedifference between the output magnitude of a reference device 17forsetting the desired speed and the output value from atachometer-generator l8 driven by the motor 7. The phase-advancingdeterminator 23, which is controlled by the speed, is shown in thedrawing connected between the tachometer 20 and the switching device 13.This is particularly advantageous at high speeds.

Assume that the motor in FIG. 7 is standing still and the desired valuen); of the speed is set about half the maximum speed in clockwiserotation when the feeding voltage of the current converter 10 isconnected. The output of the speed regulator I5, of known proportionalor proportional-integrating type, increases to a maximum correspondingto the maximally obtainable value of the difference I, between thewinding current I,,,,,, at a half period of increasing permeance and thewinding current I at decreasing permeance. At least one of the threeunit rotors is always in such a position, in the following calledpull-in position, that excitation of the corresponding stator results ina torque operating in clockwise direction. The position responsivedevice indicates at which moment a unit motor comes into pull-inposition and the switching device 13 then emits the current order 1 I Ias referencevalue for the corresponding winding current. Motor unitswhich are not in pull-in position are at the same time supplied with awinding current delivered by a corresponding converter, the currentbeing determined by the current reference I wherein I, I,,

A driving torque now arises which, besides balancing the load torque, isable to accelerate the motor. As soon as the next rotor unit comes intopull-in position, its converter receives the current order I and a motorwhich leaves the pull-in position (comes into pull-out position), issupplied through its converter with a phase winding current determinedby the current order I In stable condition, when the motor has reachedthe desired speed, the regulator 15 reduces I to such a value that themotor torque, which is a direct function of I is exactly sufficient tobalance the load torque and neither acceleration or retardation takesplace.

If the speed of the motor is considerably higher than the desired valuen which may occur upon a sudden decrease of m; or even upon a suddendecrease in the load torque, the output signal of the speed regulator 15will be negative. This is interpreted by the switching device 13 in amanner which is reproduced in FIGS. 7A

- and 78 where 7A corresponds to pulling in and 78 to drawing out. Thecurrent desired value for motor units in pull-in position is I whereasfor phases in draw-out position a higher value of I II I is obtained. Abraking moment is thus created in the motor. The motor retards and whenthe desired lower speed has been achieved, a new equilibrium is reachedas has been described in connection with the start of the motor.

The current and voltage progress for a motor unit during driving isshown schematically in FIG. 7C and during braking in FIG. 7D.Corresponding rotor positions are suggested at the top of FIG. 7C, and Uand I are the phase voltage and phase current, respectively. For thesake of simplicity I is assumed to be 0.

At high speeds the delay between current order and 0' current will be anot inconsiderable part of the period and an antecedent current order inrelation to the alternation between draw'out and pull-in position (orvice versa) may therefore be advisable. This antecedence is expressed bythe phase advance angle 0: in the drawings 7C and 7D. or is preferablymade proportional to the speed of rotation n (see the phase advancingdeterminator 23 in FIG. 7).

The converter It) shown in FIG. 7 is as shown in FIG. 9 where 25designates a control angle device, known per se, for convertingalternating current to DC pulses, and 26 are thyristors.

If the feeding network is a three phase network a converter Ida is usedfor each motor unit, said converter being in accordance with FIG. 9awhere the corresponding control angle device, which is of known design,is designated 25a and the three-phase network 9a.

If the feeding network is a DC network, the converter equipment shown inFIG. 10 is preferably used where 27 and 28 are so-called extinguishablethyristors, i.e., each thyristor is provided with a control terminal forignition and also one for extinguishing. The device also includes twodiodes 29.

At driving and maximum motor speed, the thyristor 2'7 is controlled insuch a way that it is continuously conducting when the rotor is in pullin position, whereas in draw-out position the winding current is reducedto a low value by a number of connections and disconnections carried outby the thyristor 28, usually in such a way that the blocking periods ofthis are considerably longer than the conducting periods. At everycurrent interruption in the thyristor 28, the current continues to flowthrough the winding 8 since an electromotoric force is induced in this,partly because of self-induction and partly because of permeancedecrease, and this current is fed by means of the diode 29 into thenetwork. If I 0 (in a similar manner as shown in FIGS. 7C and 7D) isdesired, the thyristor 28 is controlled in such a way that it isblocking during the entire drawing-out period. The desired value Idetermines the length of the conducting intervals of the thyristor 27during a pull in period.

FIG. 8 shows a detailed diagram of connection with reference to FIG. 7and it shows the internal connection of the devices which in FIG. 7 areindicated as blocks or circles. The comparison device 16 in FIG. 7 is inFIG. 8 included in the regulator unit and therein denoted by the tworesistors 31 and 32. The switching device 13 in FIG. 7 is in FIG. 8divided into two parts 113a and 13b from which 13b contains a switchingcontact for feeding the output signal IRY to the regulator It. Theconverter 10 is explained in detail in FIGS. 9, 9A and It). Thecomparison device 12 of FIG. 7 is included in the regulator II anddenoted III-12 in FIG. 8. The phase shifting device 23 is insertedbetween the position responsive device 29 and the switching device 13 inorder to define the angle oz shown in FIGS. 7C and 7D. In order to havea somewhat better survey, the device is divided up in a number of partsin FIG. e, such as 23 a-f. All these parts are most evident to a personskilled in the art and can be carried out in a number of ways, andtherefore it seems unnecessary to describe this specific performance. Bymeans of a potentiometer 3d the phase shifting device 23 can be adjustedto give a desired relation between motor speed and the angle 01, shownin FIGS. 7C and 7D. The devices 23a, 23b, 23c, 23d, 21% and 23f togetherconstitute the device 23 of FIG. 7. By means of a potentiometer 30 thephase advancing determinator 23 can be adjusted to give a desireddependency between motor speed and the phase advance angle a shown inthe drawings 7C and 7D. The reference numbers 31 60 designate resistors,the numbers 611 62 capacitors and the numbers 65 76 amplifiers. Thereference numbers 7 7., 78, 79 designate three different relays, thenumber 78 being used in two different place for one and the same relayin order to simplify the drawing. The timing device Ed is shown as adevice known per se including a pair of magnetodiodes for each of thewinding phases, that is for each of the three rotor units 7r. Theconnection line 100 has three conductors, each connected to acorresponding pair of magnetodiodes, but only one of these connectionsis shown in the drawing. The three pairs of magnetodiodes are arrangedso near a rotating disc 99 that their conductivities are determined byits position, the disc being furnished with permanent magnet poles andmechanically connected to the rotor 7r by a gear transmission 103 givingthe disc a higher number of revolutions than that of the rotor 7r. Thenumbers 91 96 designate zenerdiodes.

I claim:

A. Driving system intended for a power of at least 0.5 kW and comprisinga reluctance motor, the stator (4) of which has a number of stator polebodies arranged circumferentially one after the other and supporting astator winding (6) and the rotor (7) of which has a plurality of rotorpoles arranged circumferentially one after-the other with a constantpole pitch, the permeance between a rotor pole and the stator alwayshaving its maximum value when the rotor pole is substantially opposite astator pole;

B. speed measuring means (18) for furnishing a signal representative ofthe speed of said rotor;

C. a rotor position responsive pulse device (20);

D. a current source (9);

E. a controllable semiconductor converter (10) with input-, outputandcontrol terminals and having two possible power directions and onecurrent direction only;

F. first connecting means connecting the input terminals of saidcontrollable converter to said current source;

G. current transducing means (19) having input and output terminals;

H. second connecting means including said current transducing means andconnecting the output of said controllable converter to the winding ofsaid reluctance motor;

I. a closed control circuit (Y) including said controllablesemiconductor converter (10), a current comparison device (12) withterminals for a current reference value (IRY), and a negative feedbackconnection between said current transducing means (19) and said currentcomparison device J. a two-position, pulse-controlled reference valueswitching means, having an output terminal, a control terminal and firstand second input terminals, the magnitude of the input value of saidfirst input terminal determining the output value during one controlpulse, and the said second input terminal determining the output valueduring the next control pulse;

K. a first electrical circuit connecting the control terminal of saidswitching means with said rotor position responsive pulse device (20);

L. a first reference value transmitter (17) for supplying a motor speedreference value;

M. a speed comparison device (16) connected to the output of said firstreference value transmitter (17) and the output of said speed measuringmeans (18) for furnishing an output signal representing thedifferencetherebetween;

N. a second electrical circuit (15) connecting the output of saidspeed-comparison device (16) to said first input terminal of theswitching means O. a second reference value transmitter (14) connectedto the second input terminal of the switching means;

P. said rotor-position responsive pulse device (20) including means tosupply two pulses at each passage of a rotor pole in relation to astator pole, one of said pulses being emitted half a rotor pole-pitch inadvance and the other pulse half a rotor polepitch after the occurrenceof said maximum value of the permeance.

2. Driving system according to claim 1, in which the output terminal ofsaid rotor position responsive pulse device (20) is connected to'thecontrol terminals of said switching means (13) through a phase-advancingdeterminator (23), having a control terminal connected with an outputterminal of said speed measuring means (18).

1. A. Driving system intended for a power of at least 0.5 kW andcomprising a reluctance motor, the stator (4) of which has a number ofstator pole bodies arranged circumferentially one after the other andsupporting a stator winding (6) and the rotor (7) of which has aplurality of rotor poles arranged circumferentially one after the otherwith a constant pole pitch, the permeance between a rotor pole and thestator always having its maximum value when the rotor pole issubstantially opposite a stator pole; B. speed measuring means (18) forfurnishing a signal representative of the speed of said rotor; C. arotor position responsive pulse device (20); D. a current source (9); E.a controllable semiconductor converter (10) with input-, output- andcontrol terminals and having two possible power directions and onecurrent direction only; F. first connecting means connecting the inputterminals of said controllable converter to said current source; G.current transducing means (19) having input and output terminals; H.second connecting means including said current transducing means andconnecting the output of said controllable converter to the winding ofsaid reluctance motor; I. a closed control circuit (Y) including saidcontrollable semiconductor convertEr (10), a current comparison device(12) with terminals for a current reference value (IRY), and a negativefeed-back connection between said current transducing means (19) andsaid current comparison device (12); J. a two-position, pulse-controlledreference value switching means having an output , terminal (101), acontrol terminal (102) and first (103) and second (104) input terminals,the magnitude of the input value of said first input terminaldetermining the output value during one control pulse, and the saidsecond input terminal determining the output value during the nextcontrol pulse; K. a first electrical circuit connecting the controlterminal of said switching means with said rotor position responsivepulse device (20); L. a first reference value transmitter (17) forsupplying a motor speed reference value; M. a speed comparison device(16) connected to the output of said first reference value transmitter(17) and the output of said speed measuring means (18) for furnishing anoutput signal representing the difference therebetween; N. a secondelectrical circuit (15) connecting the output of said speed-comparisondevice (16) to said first input terminal of the switching means (13); O.a second reference value transmitter (14) connected to the second inputterminal of the switching means; P. said rotor-position responsive pulsedevice (20) including means to supply two pulses at each passage of arotor pole in relation to a stator pole, one of said pulses beingemitted at a first rotor position corresponding to said maximum value ofthe permeance and the other pulse at a second rotor positionsubstantially half a rotor pole pitch behind said first rotor position.2. Driving system according to claim 1, in which the output terminal ofsaid rotor position responsive pulse device (20) is connected to thecontrol terminals of said switching means (13) through a phase-advancingdeterminator (23), having a control terminal connected with an outputterminal of said speed measuring means (18).